High performance snow skis are carefully designed in order to give the user maximum control during skiing. This includes designing skis to cleanly "carve" turns; that is, during the carving of a turn, every point on the edge of the ski is designed to pass over a single point on the snow. In order to accomplish this, skis are shaped with curved edges, such that the waist portion of the ski is narrower than the shovel or tail portions of the ski. In addition to the exterior shape of the ski, the structural core of the ski is carefully tailored such that the ski has the ability to smoothly flex over its length during the carving of a turn. The shape and structural core of snowboards are also designed to cleanly carve turns. Snowboards generally have curved edges and a waist portion that is narrower than the front or rear portions of the board.
During skiing or snowboarding, the ski or snowboard flexes continuously, both in response to irregularities in the snow and in response to the user's movements, such as during turning. In addition to flexing, skis and snowboards are subjected to vibrations caused by contact with the snow, irregularities in the snow, bumps or moguls, foreign objects, etc. These vibrations can cause the bottom and edges of a ski or snowboard to lose contact with the snow, affecting the ski's or snowboard's ability to cleanly carve turns. This loss of contact with the snow thus affects the skier's or snowboarder's ability to accurately control the path of the skis or snowboard, thus affecting overall performance.
In addition to affecting performance, vibrations within skis or snowboards cause noisy chattering that can be annoying or unsettling to the skier or snowboarder. Such vibrations can also travel into the bindings, boots and the user's legs resulting in discomfort.
Skis and snowboards vibrate in bending modes at particular resonant frequencies that can be predicted analytically or measured experimentally. The deformed shape of a ski or snowboard subject to a vibration differs, depending upon which resonant frequency the ski or snowboard is vibrating at. A ski or snowboard's resonant frequencies are a function of the length, width, thickness and stiffness of the ski or snowboard. Thus, the resonant frequencies are influenced by both the internal structure as well as the geometry of the ski or snowboard.
As illustrated in FIGS. 1A-E, an exemplary ski 10's deflected shape depends upon the resonant frequency at which the ski is vibrating. FIGS. 1B-E show the deformed shape of the central axis 12 of the ski 10 at four resonant frequencies. The resonant frequencies at which the ski vibrates during actual use depends upon both the geometric and structural characteristics of the ski and external conditions, including snow conditions and surface irregularities, such as whether the ski is being used on powder, hardpack, or on ice. Generally, the skis' first three resonant frequencies are most important, as they occur the most often and are most detrimental to the ski's ability to maintain controlled contact with the snow.
In addition to longitudinal flexural vibrations produced by beam bending as illustrated in FIGS. 1A-E, skis are also subject to torsional deflections and vibrations. Torsional vibrations affect a ski's performance in a similar manner as flexural vibrations, by affecting the contact between the bottom and edges of the ski and the snow.
Snowboards also vibrate due to longitudinal flexural vibrations during use. In a manner similar to that described above with respect to skis, snowboards vibrate at resonant frequencies that produce particular displacements or mode shapes. In addition, snowboards are also subject to torsional deflections and vibrations. Due to the greater width of a snowboard, torsional vibrations can produce a more pronounced effect on a snowboard's performance than torsional vibrations produced in snow skis.
The occurrence of and resulting effects on performance of both flexural and torsional vibrations in skis and snowboards is widely recognized in the industry. Reducing the effects of both longitudinal flexural and torsional vibrations has been and still is the subject of a great deal of research and development in the ski and snowboard industry. Prior proposed solutions include incorporating the use of viscoelastic or mechanical-type dampers into the structure of the skis or snowboards. U.S. Pat. Nos. 5,332,252 (Le Masson et al.) and 5,342,077 (Abondance) are two examples of patents disclosing skis or snowboards with vibration dampening or absorption devices. Unfortunately, none of the prior developments have been suitably effective in reducing or eliminating undesirable vibrations.
Most prior art ski vibration damping systems have incorporated viscoelastic damping devices. Such systems have tended to add significant weight to the ski and have been marginally effective. In addition, past ski vibration damping systems have been broad band dampers that do not discriminate with respect to the frequency or frequencies they dampen.
As can be seen from the above discussion, there exists a need for an improved system to reduce vibrations within skis and snowboards. The present invention is directed toward fulfilling this need.